With continuous reductions in the sizes of semiconductor devices, enhancing the carrier mobility of the channel becomes very important. In the design of a stress layer of a substrate, different materials have different characteristics such as lattice constant, dielectric constant, forbidden gap, particularly carrier mobility, etc., as shown in Table 1 below.
TABLE 1LatticeDielectricForbiddenMobility (cm2/V-s)Materialconstant (nm)constantgap(eV)electronholeSi0.543111.81.121600430Ge0.5675160.6639001900GaAs0.565312.41.429200400InAs0.605814.80.3640000500InSb0.64817.70.1777000850
It can be seen from Table 1 that among the above-mentioned possible materials used as substrates, Ge has the highest hole mobility and a relatively higher electron mobility. Using Ge as the substrate of a semiconductor device will greatly enhance the carrier mobility, thus enabling manufacture of a higher-speed large scale integrated circuit (LSIC).
Further, it can also be seen from Table 1 that Ge has a lattice constant similar to that of the material Si so that Ge can be easily integrated on a Si substrate, which is commonly used in the semiconductor industry. Also by using Ge in the substrate, a semiconductor device with better performance can be manufactured having improved performance at a reduced cost without making huge improvements to the process.
In the design of a semiconductor device and an integrated circuit thereof, generally a shallow trench isolation (STI) is used to manufacture the insulating isolation among a plurality of devices in the substrate. The known method for manufacturing a STI comprises first etching a trench in the substrate, then depositing an insulating film made of e.g., an in the formed trench by a process such as chemical vapor deposition (CVD). With reduction in the device size, the aspect ratio of the corresponding STI becomes larger and the step coverage of the oxide insulating film becomes poorer, that is, the oxide insulating film on top of the narrower trench may join earlier than expected while the trench below has not been completely filled; thus holes or gaps may exist in the STI, resulting in device having impaired insulating property and worse reliability.
Overall, the existing semiconductor device with a Si channel surrounded by a STI has poor performance and reliability. In order to improve the electrical performance and reliability of the semiconductor device, the carrier mobility in the channel region shall be further improved and holes in the STI shall be eliminated